The present disclosure relates to a gas turbine engine and, more particularly, to a mid-turbine frame.
A mid-turbine frame (MTF) of a gas turbine engine typically includes a plurality of hollow vanes arranged in a ring-vane-ring structure. The rings define inner and outer boundaries of a core gas path while the vanes are disposed across the gas path. Tie rods extend through the hollow vanes to interconnect an engine mount ring and a bearing compartment. The tie rods transfer loads from a bearing compartment to an outer case structure while permitting the MTF to float.
The MTF is a typically constructed from multiple arcuate segments brazed to one another to provide a full ring. One engine application has used a one-piece cast MTF, however, this application carries the load of the bearing compartment via a bolted joint to the outer case structure. The MTF has a shallow cone angle of 15°, which more efficiently transfers the load through the MTF. The MTF includes an inner flow path surface providing inlet and exit inner diameters relative to the engine axis that provide an axial length. An outer flow path surface provides an exit outer diameter relative to the engine axis. A ratio of an exit outer diameter to the axial length of 2.6 to 1, which provides a compact design suitable for loading the MTF.
The MTF is subject to thermal stresses from combustion gases along the core gas path, which may reduce operational life thereof. The MTF with bolted joint has actively cooled vanes that include serpentine cooling passages provided cooling fluid from a bleed source.
The different load paths and cooling approaches in MTF applications provide unique design challenges.